1. Field of the Invention
The present invention relates generally to detection apparatus and, more particularly, to a residual liquid detection apparatus which detects liquid such as the washing liquid or the like remaining at the bottom of bottles such as transparent bottles made of glass or the like.
2. Description of the Prior Art
Drinking water or beverages such as beer and the like are loaded into glass bottles for marketing. Such bottles pass through a washing process before filling the bottles with the liquid. Especially, recycled bottles such as beer bottle that are reused after use by the consumer require a thorough washing in view of mixtures of trash or waste often found inside the bottle. Washing is conducted with detergent liquid and clean water, and there are cases where such detergent mixed water remains in the bottle due to the incomplete rinsing. Needless to say, subsequent refill beverage is for human consumption, it is not desired that a residual waste liquid remain in the bottle prior to refilling.
As for the conventional residual liquid detection methods, there are methods that detect the residual liquid by the absorbance ratios of high frequency waves, supersonic waves, or infrared rays. In another method, residual liquid is detected by measuring the differences in the capacitance therefore a pair of electrodes. The present trend lies mainly with detection methods by the use of infrared rays.
However, when the volume of the residual liquid is large, residual liquid detection is relatively easy by any of the methods mentioned above. However, it is extremely difficult to detect very small volumes of residual liquid, although it is desired to have apparatus that will provide stable detection of very small volumes.
One reason that makes the detection of small volumes difficult is the fact that small residual liquid volumes do not readily absorb light rays. A second reason is that the containers (mostly glass bottles) in which the liquid is filled, also absorb, to a certain extent, the light rays which pass through them. It is often the case that the light rays received on the photoelectric transducer sensor varies depending upon the container wall thickness as well as the applied color of the container.
In order to detect very small volumes of the residual liquid, it is necessary to amplify and magnify the subtle variations in the output voltage from the photoelectric transducer. Such amplified magnification of the variation at the same time magnifies variations due to the passage of transient light through the container walls, and accordingly it becomes difficult to detect the true variation of the received light by the actual residual liquid. Therefore, there is a limit to the accuracy in the detection of very small volumes of residual liquid, and it is the present practice to accept such detection when the residual liquid is over a certain predetermined volume.